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Functional Groups in Organic Compounds

  • Last Updated : 11 Nov, 2021

A hydrocarbon is a compound made up of hydrogen and carbon, and a saturated hydrocarbon is one in which the carbon atoms are joined by only a single bond. A saturated hydrocarbon is unreactive, but when another ‘atom’ or ‘group of atoms’ is introduced, the resulting molecule becomes highly reactive. The other ‘atom’ or ‘group of atoms’ in a carbon compound is called a functional group. The various functional groups are discussed further down.

What are Functional Groups?

A functional group is an atom or a group of atoms that makes a carbon compound or an organic compound reactive and determines its properties. 

Functional groups are atoms within molecules that have distinct properties regardless of the other atoms in the molecule. In organic chemistry, functional groups are the substituent atoms or groups of atoms that are connected to certain molecules. A functional group is a group of atoms or bonds within a substance that is responsible for the substance’s distinctive chemical reactions. The halo group, alcohol group, aldehyde group, ketone group, carboxylic acid group, alkene group, alkyne group are some of the most important functional groups in organic chemistry. The following parts go through each of these groups.

Halo group

Depending on whether chlorine, bromine, or iodine atom is attached to a carbon atom of the organic compound, the halo group can be chloro (-Cl), bromo (-Br), or iodo (-I). Since the elements chlorine, bromine, and iodine are collectively known as halogen, the Chloro, Bromo, and Iodo groups are referred to as halo groups and are denoted by the symbol -X. Since chloromethane (CH3-Cl) has the chloro group, bromomethane (CH3-Br) contains the bromo group, and iodomethane (CH3-I) contains the iodo group, the halo group can be found in chloromethane, bromomethane, and iodomethane. The halogen group is another name for the halo group. The halo group is the abbreviation for the halogen group. 

Haloalkanes are formed when one hydrogen atom in an alkane is replaced with a halogen atom. Haloalkanes have the general formula CnH2n+1X, where X represents the halogens. R-X is the formula for haloalkanes, where R is an alkyl group and X is the halogen atom. Halogen atoms (Cl, Br, or I) serve as the heteroatom in haloalkanes.

Alcohol group

One oxygen and one hydrogen atom are joined together to form the alcohol group (-OH). The alcoholic or hydroxyl group is another name for the alcohol group. Alcohols are organic compounds that include the alcohol group. Any class of organic compounds that include one or more hydroxyl (OH) groups linked to a carbon atom of the alkyl group is an alcoholic group. 

Alcohols are organic water (H2O) derivatives in which one of the hydrogen atoms has been replaced by an alkyl group, which is often represented by R in organic structures. 

The ethyl group, for example, is the alkyl group in ethanol C2H5OH (or ethyl alcohol). Alcohol is made by replacing a hydroxyl group with one hydrogen atom in an alkane. The homologous series of alcohols have the general formula CnH2n+1OH.

Among the most common organic compounds are alcohols. They are employed as sweeteners and in the manufacture of perfumes, as well as being important intermediates in the synthesis of other compounds. They are also among the most widely produced organic chemicals in industry. Ethanol and methanol (or methyl alcohol) are two of the most well-known alcohols.

Aldehyde group

One carbon atom, one hydrogen atom, and one oxygen atom are joined together to form the aldehyde group (-CHO). Any organic compound in which a carbon atom has a double bond with an oxygen atom, a single bond with a hydrogen atom, and a single bond with another atom or group of atoms (designated R in general chemical formulas and structure diagrams) is called an aldehyde.

All aldehydes contain the carbonyl group, which is a double bond between carbon and oxygen.

Aldehydes have the general molecular formula CnH2nO, where n is the number of carbon atoms in one molecule. Many aldehydes have pleasant scents, and they are created by dehydrogenation (removal of hydrogen) from alcohols, which is how the term “aldehyde” was derived. The two simple aldehydes are formaldehyde HCHO also known as methanal and acetaldehyde CH3CHO also known as ethanal.

Ketone group

One carbon atom and one oxygen atom make up the ketone group (-CO-). The presence of a carbonyl group, in which the carbon atom is covalently bonded to an oxygen atom, distinguishes ketone from other organic molecules. The carbon atom is joined by a double bond to the oxygen atom. The alkyl groups or hydrocarbon radicals (R) form the remaining two bonds. 

Since a ketone group is always found in the middle of a carbon chain, a ketone must have at least three carbon atoms in its molecules, one ketone group carbon atom, and two carbon atoms on both sides. Ketones with less than three carbon atoms are not really possible. 

Ketone has the general molecular formula CnH2nO where n is the number of carbon atoms in one molecule. The simplest ketone is acetone CH3COCH3, also known as propanone. The physiological effects of ketone molecules are significant. They can be present in a variety of sugars as well as pharmaceutical chemicals such as natural and synthetic steroid hormones. The anti-inflammatory drug cortisone contains three ketone groups in its molecules.

Carboxylic Acid group

A carboxylic acid is an organic molecule with a carbon (C) atom double-bonded to an oxygen (O) atom and a single-bonded hydroxyl group (OH). The carbon atom is linked to a hydrogen (H) atom or another univalent combining group by a fourth bond. The carbonyl (C=O) and hydroxyl (-OH) groups make up the carboxyl (-COOH) group. 

Carboxylic acids, often known as organic acids, are organic molecules that include the carboxylic acid group. Carboxylic acids are sometimes known as alkanoic acids.

The homologous series of carboxylic acids have the general formula R-COOH, where R represents an alkyl group. Acetic acid CH3COOH also known as ethanoic acid is the most common carboxylic acid. Acidity is the most important chemical property of carboxylic acids. They are more acidic than other organic compounds with hydroxyl groups but less acidic than the well-known mineral acids.

Alkene and Alkyne groups

The alkene group is a carbon-carbon double bond. The alkene group is present in ethene and propene among others. The compounds containing the alkene group are known as alkenes. The homologous series of alkenes have the general formula CnH2n, where n is the number of carbon atoms in one molecule.

The alkyne group is a carbon-carbon triple bond. The alkyne group is present in ethyne, and propyne among others. The compounds containing the alkyne group are known as alkynes. The homologous series of alkynes have the general formula CnH2n-2, where n is the number of carbon atoms in one molecule.

Sample Questions

Question 1: Write the molecular formula for the alcohol group with 4 carbon atoms.

Answer:

The molecular formula for the alcohol group is CnH2n+1OH. If there are 4 carbon atoms then n=4, this means C4H2(4)+1OH or C4H9OH. So the required molecular formula is C4H9OH

Question 2: Can the compound C2H4O be a ketone group?

Answer:

A ketone must have at least three carbon atoms in its molecules, one ketone group carbon atom, and two carbon atoms on both sides. Ketones with less than three carbon atoms are not really possible. In the given compound, we have 2 carbon atoms, so it is not a ketone group.

Question 3: What is the molecular formula of aldehyde which is derived from butane?

Answer:

Aldehydes have the general molecular formula CnH2nO, where n is the number of carbon atoms in one molecule. Since butane C4H10 has 4 carbon atoms, so n=4, this means C4H2(4)O or C4H8O. Hence the molecular formula of aldehyde which is derived from butane is C4H8O.

Question 4: Identify the functional group present in the compound C3H8O.

Answer:

In the given compound C3H8O, the number of carbon atoms is 3, so n=3. First check if it satisfies the molecular formula of alcohol, aldehyde, ketone, or carboxylic acids. Since it has only one oxygen atom, so it cannot be a carboxylic group. Alcohol has the general molecular formula CnH2n+1OH, where n is the number of carbon atoms in one molecule. Put n=3 in this formula, we get C3H2(3)+1OH or C3H7OH or C3H8O which matches the given compound. So the given compound have alcohol as its functional group.

Question 5: Write the molecular formula for the alkene group and alkyne groups containing 5 carbon atoms.

Answer:

Given that there are 5 carbon atoms, so n=5. Alkenes have the general formula CnH2n, where n is the number of carbon atoms in one molecule. Put n=5 in this formula, C5H2(5) or C5H10.

Alkynes have the general formula CnH2n-2, where n is the number of carbon atoms in one molecule. Put n=5 in this formula, so C5H8 or C5H8.

Hence the molecular formula for the alkene group is C5H10 and the alkyne group is C5H8.


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